In the art of punch or arbor presses, such presses are designed for exerting a maximum downward force on a piece of sheet metal for the purpose of shearing, forming or drawing it. Such presses are normally rated by the maximum force in tons such as 25 ton, 50 ton, 100 ton or the like, which the press can safely exert.
The maximum force required to perform a particular operation on a piece of sheet metal can normally be calculated by determining the area of the metal to be acted on multiplied by a coefficient expressing the resistance of such metal to the type of deformation to be effected.
Ordinarily the largest area to be effected is in originally blanking out the piece to be formed from a base sheet of metal. In such case, the area to be cut or sheared from the base sheet metal equals the perimeter of the cut multiplied by the plate thickness and is normally greater than the area of any subsequent forming operation on the blank. Thus, if a piece of sheet metal is to be blanked out and then formed in the same punch press, the press will have to be rated at a force equal to that required to effect the blanking out operation. Thereafter, for the subsequent forming operations the press will only be operating at a fraction of its maximum rated capacity.
Oftentimes in manufacturing plants, it is desired to use a punch or arbor press large enough to do the subsequent forming operation but not large enough to do the blanking out operation. The invention is particularly applicable to such a situation and enables the use of a punch or arbor press having a rated capacity insufficient to perform the required blanking operation but a sufficient capacity to perform the forming operation.